Or: A Giant Pain In The Tookus
So let's get this out of the way: Thiazi is a made up, not real, never was, fictional myth. Aside from that, the storm giant did some pretty ballsy stuff way back in pre-Internet Norway. (A very dark and scary time, indeed.)
Thiazi's father was Olvaldi and his mother was, frankly, exhausted. He grew up in Jotunheim, the land of the giants, on a mountain called Thrymheim. When his father died, he and his two brothers divvied up the property by each taking a big mouthful of gold. He also had a daughter named Skadi (who wasn't exactly the nicest lady on the block herself.)
Little known fact: Giants are experts in magic. So one day Thiazi decided to change teams and disguised himself as an eagle. He flew to Midgard where Loki, Honir, and Odin were having a barbecued ram. He sat down beside them and asked for a bite to eat, and - since talking eagles were hardly as big a deal then as they are now - they agreed.
The little eagle kept eating and eating, until finally Loki decided that the bird had had enough. They argued a bit, and Thiazi ended up being stabbed by Loki's staff. Enraged, Thiazi flew off with the staff (and Loki) in tow. Loki tried and tried to break free, but finally he gave up. Thiazi let him leave on one condition: that Loki bring him Idun and her "apples of youth", if you know what I mean.
Loki, being the sniveling simp that he was, agreed and returned to Asgard. He went to Idun's little house in the 'burbs and convinced her he had found another tree that grew golden apples in Midgard. (Note to Idun: I've got a bridge in Brooklyn for sale cheap!) She went out to Midgard and was promptly snatched up by Thiazi.
Little known fact #2: A golden apple a day keeps the aging away. Without Idun and her apples, the gods of Valhalla quickly began to fade away. Not being total suckers, blame quickly fell on Loki, who admitted he had helped the giant carry Idun off. Threatened with death, Loki promised to return Idun to her rightful place.
So Loki turned himself into a falcon and flew to Thrymheim, where he located Idun and - get this - turned her into a nut and flew the coop. Thiazi came home, discovered the deed, and took off after the airborne Viking. Just as Loki made it over the Asgard walls, Odin and Co. lit a huge bonfire they had built, and the impending fire and smoke badly burnt Thiazi, who fell to the ground and was stomped out (!) by Thor. They've got tough no-smoking ordinances in Asgard.
Later, when Skadi came looking for revenge, Odin appeased her by throwing Thiazi's eyes into the sky and turning them into stars - which, now that I think about it, is really creepy.
Source: http://www.pantheon.org/articles/t/thiazi.html. BONUS FUN TIME: Find all 5 NFC pipelinks.